Those issues aside, I'm kind of worried that an online format won't allow enough access to the instructors.
A masters degree isn't about being taught by instructors it is about self learning. The instructors are only there for guidence or to ask the odd question. You should be able to watch the lecture material and then go away and research / do your project on your own with only minimal instructor interaction.
Right. Correct me if I'm wrong, but don't MS students still typically work under a faculty member related to their focus? So it would still be important to have that one-on-one interaction, right?